Suppression of Core Polarization in Halo Nuclei

Halo nuclei are studied using a $G$-matrix interaction derived from the Paris and Bonn potentials and employing a two-frequency shell model approach. It is found that the core-polarization effect is dramatically suppressed in such nuclei. Consequently, the effective interaction for halo nucleons is almost entirely given by the bare $G$ matrix alone, which presently can be evaluated with a high degree of accuracy. The experimental pairing energies between the two halo neutrons in ${}^6\mathrm{He}$ and ${}^{11}\mathrm{Li}$ nuclei are satisfactorily reproduced by our calculation. It is suggested that the fundamental nucleon-nucleon interaction can be probed in a clearer and more direct way in halo nuclei than in ordinary nuclei.